Turned out to 2.5 with no other changes last night and went for a test ride. Power curve seemed good, throttle response was pretty crisp but could be crisper I know. I do need to put in a fresh plug since it's been through a few changes since last one - cheap baseline insurance.

KLXster, I looked through your threads and it's all interesting stuff. I'm unlikely to get that scientific about it, but it's good stuff to include in the thought process while fiddling with this bike. I think I will add an aftermarket header at some point and in the meantime I will port match the header. I do that on chainsaws to smooth that exhaust flow and it makes a massive difference along with porting the mufflers. From another discussion on smoothing the header flange interior I am planning to add a small MIG bead outside the flange so there is no chance of failure once the interior is relieved. I know you've had no issues but I'd rather do 20 minutes of extra work than push the beast back to the truck with a busted header some day.

I'm thinking of the FSW header as I think it is straightforward in design and can use a stock heat shield if I remember right. Anyway, that's part of the next evolution and I have not made any final decisions.

Here's a question for everyone: what octane fuel is everyone using? I religiously use only non-ethanol fuel in my saws and outboards. Wondering what the general opinion is on fuel quality and octane rating for these little 4-strokes.

 

That's good to know!

 

87

sometimes 89 if its really hot out. That is RON+MON/2 standard US AKI octane rating of course.

 

The only non ethanol fuel I can get is 91 octane. The 331 runs noticeably better with the non ethanol fuel.

 

Hoots, If I had it to do over, I would not port match the header. While I did not dyno test the port match, I lost low end torque and throttle response - I was not happy with the bikes' performance.
It is not intuitive, but the header flange size/shape seems important for lower rpm torque and throttle response.
Perhaps the upper rpm power improved - after getting the AFR rich enough - more than w/o a port match but I really don't know.

The bike didn't really come alive until I got the AFR down below 14:1.

You don't have to fret over the carb setup - I've done the leg work. Yank the lid, do the #132, set needle up one from stage II instructions, and you'll giggle like a little girl every time you wind it up.

 

I wonder if the stock header provides the right level of turbulence and back pressure from the outset, and all this rushing around getting wide open header pipes is just creating more work getting the jetting and mix right (maybe too much for a 250cc engineered bike anyway). I know you can really mess up a chainsaw by opening up the exhaust/header too much - need to go to a max of about 85% of the exhaust port opening as your muffler exit port. If you open it further there isn't enough back pressure and you lose performance in a hurry (and blow pistons). If you nail it you get awesome throttle response and increased cutting power at WOT. Of course those are 2-strokes.

Anyway, I'm going to run non-ethanol with a fresh plug and this jetting for a while, then think about dumping the airbox lid, or doubling up snorkels, and increasing the jet size. Not sure I want to go completely lidless with as much water as we have around here. Hate to drown my engine when there are alternatives.

Is anyone with a DG running a smaller diameter quiet tip, or just wide open stock muffler tip? The stock opening is pretty damn big - I think it could be necked down with a tip to maybe 1 1/4" or 1 3/8" and still have a nice note without shaking the leaves off the trees.

 

Louder is better imo

 

Keep in mind the EZ-just has nothing to do with your main jet/high rpm circuitry. You seem to be implying you can lean out the 128 with the EZ-just and that's not going to have an effect.

 

Hang on. Enlighten me then. You're saying that adjusting the fuel/air mix at the screw doesn't affect the rich/lean condition of the fuel system with a given main jet? I'm asking that honestly because that disagrees in part with what I know. I know there's a finite range with any given main jet and one may have to upsize or downsize because you can only affect mix so far before your bloody mix screw falls out.

And are you saying that's that just for certain RPM ranges or globally?

Maybe I am coming at this from a simplistic 2-stroke mindset but I just went through this same set of issues with a quad carb on my old Yamaha 4-stroke, 4 cylinder street bike and there was purportedly a critical affect on rich vs. lean with the mixture screws when balancing/syncing them. That all worked out and the bike absolutely screamed in the end.

I'm interested to hear any and all input on this one.

 

HOots, I missed that you are toying with the mixture screw thinking that you are adjusting the AFR over the entire range of RPM. That thinking is too far away from being correct for me to have picked up on.. Please take the time to research for yourself that the mixture screw only affects idle to off idle transition .